Starting with house vs start battery

[SPembleton]

I have 2 house batteries and 1 starting batttery.  I try to remember to switch to the start battery under power and then switch to house when i shut off the engine, but i sometimes forget to switch back to house after shutting off the engine..  What is the problem with using the house batteries for starting and general usage, and keeping the remaining battery just as a backup if needed?

[sailaway]

Nothing sounds like a good idea. Charlie

[Ken Juul]

The engine doesn't care which battery you use.  It is the rest of the stuff on the boat. 
The issue I was having was losing the chartplotter when starting the engine (temp low voltage).  Ok for home port, not so much entering an unknown port or if you have a guest driving.  I have a separate start circuit with its' own battery switch.  Start battery always starts the engine, house bank runs everything else.  In emergencies, I can start with the house, or run the house with the start. 

[mark_53]

I have 2 house batteries and 1 starting batttery.  I try to remember to switch to the start battery under power and then switch to house when i shut off the engine, but i sometimes forget to switch back to house after shutting off the engine..  What is the problem with using the house batteries for starting and general usage, and keeping the remaining battery just as a backup if needed?

It sounds like you don't have an ACR installed. You should not have to turn off the start battery when the engine is turned off.

[KWKloeber]

Steve

No problem.  Read the 101 topics -- and the analysis by MaineSail of what it takes to start a diesel. There is no need for a "start" battery -- instead think of it as an "emergency reserve" and just use your bank for starting.

Are you on a mooring or tied to shore power? If the latter, your emergency battery will alyways be topped off and so (generally) you don't need to switch to charge it. KISS

ken

..  What is the problem with using the house batteries for starting and general usage, and keeping the remaining battery just as a backup if needed?

[mark_53]

What is the problem with using the house batteries for starting and general usage, and keeping the remaining battery just as a backup if needed?

If you have an automotive type battery as a start battery, it makes sense to use the start battery for starting and save the Ah for the house bank since the start battery is not a deep cycle. If the start battery is deep cycle, like the house, then it doesn't make too much difference but you'll do more switching. I like to set my house bank to 1 on the 1-2-B and leave it there. The start battery switch is turned off only when leaving the boat for an extended time or working on the engine.

[KWKloeber]

READ THE 101, and learn how many "A-Hs" you use up starting the engine!!

How does being a non D.C. battery's an argument for using it for every start?  Without sensitive equipment it's difficult to even MEASURE the amt of energy used to start the engine!!!

If you have an automotive type battery as a start battery, it makes sense to use the start battery for starting and save the Ah for the house bank since the start battery is not a deep cycle.

[mark_53]

READ THE 101, and learn how many "A-Hs" you use up starting the engine!!

How does being a non D.C. battery's an argument for using it for every start?  Without sensitive equipment it's difficult to even MEASURE the amt of energy used to start the engine!!!

It's a matter of using your equipment as it was designed.  An automotive type start battery is designed for short bursts of high energy. If you have spent the time, energy and cash to install a start battery, then why not use it? If it just sits there, your not getting use.  Boaters look for all sorts of ways to conserve power so why not use the equipment you have?  The OP was concerned with all the switching he was doing. I'm saying the switching is not necessary if you have the right setup.  Better to keep whatever amount of Ah the starting battery requires in the house bank where greater demand will be and used how the house bank was designed.

[KWKloeber]

Again, think  designed for RESERVE, not start!!

Do you know how many A-Hs your saying you are "keeping" for the bank???? Keep this Fact based -- look it up.

Ok, I'll make a counter argument. Keeping the third battery for "emergency" -- what kills a battery? Number of cycles, correct?   So the less you use it the greater chance it will be "like new" when you need it for an emergency. 

You said "if it's an automotive rather than deep cycle battery."  What difference would that make using your argument of "saving" amp hours in the house bank?   The third battery is irrelevant in that logic thread.   

Use the facts to make your case.....  starting uses LESS than 1/10 amp hour. Out of say a 150 ah bank.  Save that? Really?  That's LESS THAN 0.000667 percent used. Putting it into perspective, that's equivalent to stopping at grocery store A versus grocery store B to save one penny on a $15 steak.  Your steak, your choice.

Steve,  just do what you proposed. You're  thought process is absolutely "right on" for your situation/set up.

kk

READ THE 101, and learn how many "A-Hs" you use up starting the engine!!

How does being a non D.C. battery's an argument for using it for every start?  Without sensitive equipment it's difficult to even MEASURE the amt of energy used to start the engine!!!

It's a matter of using your equipment as it was designed.  An automotive type start battery is designed for short bursts of high energy. If you have spent the time, energy and cash to install a start battery, then why not use it? If it just sits there, your not getting use.  Boaters look for all sorts of ways to conserve power so why not use the equipment you have?  The OP was concerned with all the switching he was doing. I'm saying the switching is not necessary if you have the right setup.  Better to keep whatever amount of Ah the starting battery requires in the house bank where greater demand will be and used how the house bank was designed.

[KWKloeber]

Steve, see

https://forums.sailboatowners.com/index.php?threads/engine-starting-video-real-world-amp-load-data.102027/

ken

[mark_53]

Again, think  designed for RESERVE, not start!!

Do you know how many A-Hs your saying you are "keeping" for the bank???? Keep this Fact based -- look it up.

Ok, I'll make a counter argument. Keeping the third battery for "emergency" -- what kills a battery? Number of cycles, correct?   So the less you use it the greater chance it will be "like new" when you need it for an emergency.

Based on your energy numbers, one would never fully cycle the start battery since it is immediately recharged.  If you never use it, your getting no use of the asset you purchased and when it truly is an emergency, you will be hoping it works.  By using it, your 1) not depleting your house bank, 2) your using your asset, 3) your confident your start battery will work when called upon and 4) It will isolate your instruments from starting transients.
[/quote]

You said "if it's an automotive rather than deep cycle battery."  What difference would that make using your argument of "saving" amp hours in the house bank?   The third battery is irrelevant in that logic thread.   

The OP question had to do with starting off the house bank and reducing switching.  Either battery type would have no problem starting the engine and the total Ah capacity of the boat is fixed.  If the start/RESERVE battery is a deep cycle, it would not make much difference which battery bank was used for starting since the reserve could be depleted for house loads as it was designed.  Not so with an automotive start battery. If the START/reserve is an automotive type start battery, one would not be happy with its deep cycle performance.  With either type battery, I would still start off the start battery to get the use out of it, have the confidence it's working and, isolate starting transients to your instruments. I would not like to flip a switch to accomplish that and is not necessary.

Use the facts to make your case.....  starting uses LESS than 1/10 amp hour. Out of say a 150 ah bank.  Save that? Really?  That's LESS THAN 0.000667 percent used. Putting it into perspective, that's equivalent to stopping at grocery store A versus grocery store B to save one penny on a $15 steak.  Your steak, your choice.

Savings add up.  Also, if you use an ACR, the two banks are combined for a period of time after charging thus getting additional use of the start battery.

[SPembleton]

Thank you all for your insights and experience.  I am having some of the same problems that Ken Juul mentioned losing power for the chartplotter (actually i lose my bluetooth wind sensor first when power drops.) I leave my boat in a slip and on shore power 24/7.  I am going to be really careful about starting on the start battery and switching to house as soon as i shut down the engine, and see if it affects the length of time before i lose power for the wind sensor. If there is no difference, I will just keep the "start battery" as emergency as KWKloeber and Mainsail suggests.  If it does make a difference i will just have to be more disciplined.  In any case, i do appreciate everyones input!

[KWKloeber]

Steve,

You've hit one nail squarely on the head. If you're tied to a shore charger,  your battery and charging set up is "correct",  it doesn't make a rats butt difference on the "start" versus "reserve" because your reserve will be fully charged every time you leave the dock.

The argument of "getting use out of "a piece of equipment is a false argument. You get use out of which ever battery you use.   A reserve battery is like a fire extinguisher you buy it for when you need it not to use it every time you want to put out a campfire. If you have a reserve tank of propane, you don't keep using it up just to "get use out of it". If you have a reserve fuel tank on a plane you don't keep using it to "get use out of it" (Other than to keep fuel fresh).

It's a different situation if you're on a hook, and have an ACR to make sure your topping off the "reserve" battery every minute you motor.

I'm not really sure how losing power to the Bluetooth makes a difference with which battery you start on?   Elaborate?

Ken.

[mark_53]

Thank you all for your insights and experience.  I am having some of the same problems that Ken Juul mentioned losing power for the chartplotter (actually i lose my bluetooth wind sensor first when power drops.) I leave my boat in a slip and on shore power 24/7.  I am going to be really careful about starting on the start battery and switching to house as soon as i shut down the engine, and see if it affects the length of time before i lose power for the wind sensor. If there is no difference, I will just keep the "start battery" as emergency as KWKloeber and Mainsail suggests.  If it does make a difference i will just have to be more disciplined.  In any case, i do appreciate everyones input!

If you use a Blue Sea SiACR (start isolation) along with running your chart plotter off your house and start off the start battery you will not have the problem of loosing your instruments when you start.  And you won't have to through any switches

[SPembleton]

I'm not really sure how losing power to the Bluetooth makes a difference with which battery you start on?   Elaborate?
Ken.

I did deteemine that when the voltage drops to 10.8v the bluetooth gWind sensor stops working.

I just want to ensure that starting on the start battery or starting in the house battery makes no difference on my boat. I agree with you in theory, but pos could have done all kinds of things from 1986.